The durability and efficiency of electrochemical cells, particularly shelf life durability, is limited by, among other factors, corrosion of the metallic anode which causes dissolution of the anode and generation of hydrogen gas. For example, in the Leclanche primary battery cell, the zinc anode undergoes corrosion in the electrolyte resulting in dissolution of the zinc and the attendant impaired efficiency of the cell. Various methods for minimizing anode attack have been attempted, for example, by means of additives to the electrolyte and by treating the anode as by coating with a material to reduce anode attack. However, such materials must be compatible with the electrochemical system, particularly in the case of materials coated on the anode, and must not so insulate the anode as to prevent its satisfactory functioning.
Mercuric chloride is one of the materials widely employed as a metallic corrosion inhibitor in batteries. However, some problems arise in connection with the use of mercury, generally as a result of the method of flat battery manufacture which may result in inadequate amalgamation of the zinc anode.
In addition, mercury embrittles thin (e.g., up to 10 mils) zinc foil which substantially obviates the use of such thin foil in batteries of the flat, planar type such as those disclosed in U.S. Pat. Nos. 3,563,805; 3,617,387; and 3,734,780 and the like.
Copending application Ser. No. 50,354 is directed to the employment of quaternary ammonium halide as an addition to an ammonium chloride electrolyte.
The essence of the invention set forth in application Ser. No. 50,354 is to reduce or eliminate the mercury compounds by the addition or total substitution of a quaternary ammonium halide which does not embrittle foil but which provides a highly effective corrosion inhibitor.
Planar batteries of the type disclosed in the aforementioned U.S. patents are particularly suitable for employment in a film pack of the type sold for use in the photographic camera sold by Polaroid Corporation, Cambridge, Massachusetts, U.S.A. under the trademark SX-70.
In such cameras, the battery, disposed as a component of a film pack for employment in and in combination with the camera, provides the electrical energy necessary to operate the camera's exposure control, film transport and photoflash systems and, accordingly, such battery is required to operate in a sequential series of power generating modes which may or may not be interrupted by more or less extended recovery and/or storage times and under which conditions to deliver the required series of high current pulses dictated by the photographic system design. However, because the battery is employed in close proximity to photographic film units, the components of the battery can deleteriously effect the photographic system. For example, ammonia from the ammonium chloride electrolyte can fog a photographic negative.